Here, it is shown three-step investigative procedures aiming to improve pentose-rich fermentations performance, involving a simple system for elevated mass production by Scheffersomyces stipitis (I), cellular recycle batch fermentations (CRBFs) at high cell density using two temperature strategies (fixed at 30°C; decreasing from 30 to 26°C) (II), and a short-term adaptation action seeking to acclimatize the microorganism in xylose rich-media (III). Cellular propagation provided 0.52gdrycellweightgRS(-1), resulting in an expressive value of 45.9gdrycellweightL(-1). The yeast robustness in CRBF was proven by effective ethanol production, reaching high xylose consumption (81%) and EtOH productivity (1.53gL(-1)h(-1)). Regarding the short-term adaptation, S. stipitis strengthened its robustness, as shown by a 6-fold increase in xylose reductase (XR) activity. The short fermentation time (20h for each batch) and the fermentation kinetics for ethanol production from xylose are quite promising.
BACKGROUND: Although cells recycling has been recognized as an important technology in obtaining first generation ethanol, there are few studies using this technology to obtain second generation ethanol, limited only to the fermentation of lignocellulosic hydrolysate and molasses mixture. The present work evaluated the use of cell recycle batch fermentation to validate a setup for cellulosic ethanol production. Setup considered a diluted phosphoric acid pretreatment followed by alkaline delignification, enzymatic hydrolysis, hexoses concentration, and finally, cell recycle batch fermentations. After the concentration step of cellulosic hydrolysate, performance of Saccharomyces cerevisiae recycling was evaluated from parameters related to the alcoholic fermentation, such as productivity and ethanol yield.
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